1. Field of the Invention
This invention relates to an extrusion process, and more particularly to an indirect hot extrusion process in which a container is moved while an extrusion die is kept stationary.
2. Description of Prior Art;
Conventionally, there have been adopted three major indirect extrusion processes. One of these conventional processes involves keeping the container freely movable during the extrusion, while the billet is pressed by a pressing stem from the opposite side to the fixed die, so that the container may be moved ahead by the static frictional force between the billet and the container, thereby effecting extrusion without causing any dynamic friction between the billet and the container. Another conventional process is characterized by the container and the main ram being held in contact with each other during the extrusion, such that the container is pushed ahead by the main ram, to thereby extrude the billet from the extrusion port formed in the front-side of the stationary die.
The third conventional process is to provide an independent cylinder for moving the container, so that the container may be moved independently even during the extrusion.
The first-mentioned conventional process has a drawback in that, as the billet in the container becomes short as the end period of the extrusion, static friction occurs between the container and the billet so that the container cannot be further moved ahead. Meanwhile, the pressurizing system thereof continues to move ahead, so that the billet is moved relatively to the container so as to cause a so-called direct extrusion effect, resulting in a deteriorated quality of the product at the end of the extrusion.
In the second-mentioned conventional process, the aforementioned relative movement does not take place. However, since the power required for the forward movement required for purposes other than the extrusion is for forward movements only, as in the first-mentioned process, it has been impossible to achieve the mutual connection of the container and the stem at the position corresponding to the length of the billet.
In the third-mentioned conventional process, the container and the ram can move together if the friction between the billet and the ram is sufficiently large. However, if the friction is too small, only the container is moved ahead, to the contrary of the first-mentioned process, so that the extrusion plate and the billet are exposed from the rear end of the container, or, alternatively, the ram is moved ahead with the container having moved to the end of its forward stroke, so as to cause the aforementioned direct extrusion effect.